1. Field of the Invention
The present invention relates to a printing apparatus, in which ink reserved or stored in an ink tank is stirred, and a stirring method in the printing apparatus.
2. Description of the Related Art
An ink jet printing apparatus for ejecting ink from a print head so as to perform printing has been widely adopted as a printing apparatus. As the ink for use in such an ink jet printing apparatus, a dye ink containing a dye as a colorant and a pigment ink using a pigment as a colorant have been used in most cases. Among these kinds of ink, in the case of a pigment ink, a pigment component may be precipitated to be coagulated in the ink when the pigment ink is left unused during a long period of time. Therefore, when the ink is ejected onto a print medium, the density of droplets of the ejected ink depends on a landing position, thereby inducing variations of the density. Consequently, a print image has inconsistencies in color or the like. The inconsistencies may adversely influence the print image.
In view of this, there has been proposed an ink jet printing apparatus in which ink is periodically stirred inside of an ink tank in order to prevent the pigment from being unevenly collected inside of the ink tank. Japanese Patent Laid-open No. 2007-331307, for example, discloses an ink jet printing apparatus in which a stirring level is adjusted according to a lapse of time after a previous stirring operation and the residual amount of ink reserved in an ink tank.
In the ink jet printing apparatus disclosed in Japanese Patent Laid-open No. 2007-331307, a carriage having a print head and an ink tank mounted thereon reciprocates along a guide shaft without performing any printing operation, thus stirring ink inside of the ink tank. Japanese Patent Laid-open No. 2007-331307 is silent about the position of the stirring operation. Normally, an ink stirring operation is performed inside of the ink tank when the carriage is moved to a predetermined position. However, in the case where the stirring operation is performed at a determined position, the sliding frequencies of members are different between the position at which the stirring operation is performed and other positions. Consequently, there arises a difference in abrasion level between the carriage and the guide shaft.
If abrasion promotes only at a part between the carriage and the guide shaft, the friction levels are different between a relatively large abraded portion and other portions. Therefore, when the carriage is moved along the guide shaft, vibrations become larger at a portion at which the abrasion level is varied, thereby inducing a possibility of degradation of landing accuracy of an ink droplet onto a print medium. In this manner, there is a possibility of degradation of the quality of a print image.